Centriugal pump

ABSTRACT

A centrifugal pump which includes a tubular structure which extends into an eye of an impeller and which directs a medium to be pumped into the eye, and wherein an axially extending annular cylindrical sealing clearance is formed between opposing surfaces of the impeller and the structure.

BACKGROUND OF THE INVENTION

This invention relates to a centrifugal pump and more particularly to aseal between opposing surfaces of an impeller and an inlet liner of thepump.

In a centrifugal pump, apart from a primary slurry flow, recirculationslurry flow takes place between a front shroud of the impeller and frontsecondary pump-out vanes, and an inlet of the pump. The recirculatingslurry flow is abrasive and degrades the pump-out vanes and the inletliner, resulting in component wear, a loss in pumping efficiency and anincrease in energy consumption.

The situation is illustrated in FIG. 1 of the accompanying drawingswhich shows in cross section a part of a typical centrifugal pump 10 inwhich recirculation of slurry leads to component wear.

The pump 10 includes an impeller 12, with vanes 14, which is mounted ona shaft in a volute 16 of a casing 18. A suction inlet 20 in use directsslurry in the direction of an axis 22 into a circular entrance area intothe impeller, referred to as an eye 24 of the impeller. A clearance 30(marked by xxx for ease of identification) is formed between a surface32 of the impeller around the eye 24 and a spaced apart surface 34 of afront liner 36. The clearance 30 forms a vertical or near-vertical (i.e.at about 90 degrees relative to the axis 22) so-called “labyrinthsealing arrangement” particularly on the radial innermost portionthereof, through which the slurry is recirculated. The opposing surfaces32 and 34 are abraded by the slurry flow, leading to the aforementionednegative consequences. In order to improve this aspect an adjustment ofthe front liner 36 relative to the impeller 12, in an axial direction,is required. This type of adjustment can be difficult to achieve.

The invention is concerned with the aforementioned situation.

SUMMARY OF THE INVENTION

The invention provides a centrifugal pump which includes a casing, avolute inside the casing, an impeller mounted on a shaft in the volutefor rotation about an axis, the impeller including a centrallypositioned eye and a plurality of vanes which extend radially outwardlyfrom the eye, and a structure which supplies a medium to be pumped intothe eye, and wherein the structure includes an outer seal surface whichextends circumferentially and concentrically around the axis, which isparallel to and concentric with the axis and which extends, at leastpartly, into the eye, and the impeller includes an inner seal surfacewhich extends circumferentially and concentrically around at least apart of the eye, and which is radially spaced from and which opposes theouter seal surface, whereby an axially extending, annular sealingclearance is formed between the outer seal surface and the inner sealsurface.

A second sealing clearance may extend outwardly from the axiallyextending annular sealing clearance at an acute angle relative to theaxis.

The axially extending annular sealing clearance may be substantiallycylindrical i.e. with outer and inner surfaces which are spaced apartand which are parallel to each other and coaxial with the axis.

The structure may supply the medium in an axial direction into the eye.

As used herein “sealing clearance” refers to an arrangement in which aseal is formed between opposing surfaces of at least two components.Such seal does however form a gap between the opposing surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe accompanying drawings in which:

FIG. 2 illustrates in cross section and from one side an end suctioncentrifugal slurry pump according to one form of the invention.

FIG. 3 is a side view in cross section and on an enlarged scale of afront liner used in the pump of FIG. 2 (Item 80 in FIG. 2 ),

FIGS. 4A and 4B depict, schematically, parts of the pump enclosed in acircle 4 in FIG. 2 , with different spacings between the parts, and

FIG. 5 depicts performance curves of a conventional slurry pump and aslurry pump of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 2 of the accompanying drawings illustrates from one side and incross section a part of an end suction slurry pump 50 according to theinvention.

The pump 50 includes a casing 52 which defines a volute 56. An impeller58 is mounted on a shaft 66 inside the volute for rotation about an axis62. The impeller 58 has a drive end 64 which is connected to the shaft66, which in use drives the impeller.

The impeller 58 defines a centrally positioned impeller eye 68, primarypump-out vanes 70, and secondary pump-out vanes 72 on a front shroud 74.

An axially directed inlet structure 78 is mounted to the casing 52. Thestructure 78 includes a tube 80 which is centred on the axis 62. Aradially extending flange 82 on the tube forms a front liner 84 for thepump. An inner surface 86 of the front liner opposes the vanes 72.

In use slurry is supplied in an axial direction through the tube 80 to adischarge outlet 88 and then into the eye 68 of the impeller. Thedischarge outlet 88 has a rounded inner surface 88A—see FIG. 3 whichshows the inlet structure 78 from one side and in cross section, on anenlarged scale.

A section 90 of the tube 80 which protrudes to the left of the flange 82has an outer seal surface 92 which is planar, which is parallel to theaxis 62 and which extends circumferentially around the axis.

In this embodiment a junction 94 between the section 90 and the flange82 has a junction seal surface 96 between the outer seal surface 92 andthe inner surface 86 of the front liner 84 which is at an acute angle 98with respect to the axis 62.

The section 90 extends into the eye 68 which is enlarged, compared to aconventional, known, design, to accommodate this feature. The impeller58 at the eye 68 has a circular inner seal surface 100 which is centeredon the axis 62 and which is concentric (maybe rather use coaxial—meaningsame axis) with the outer seal surface 92. The inner seal surface 100which is centred on the axis 62 and which is concentric with the outerseal surface 92. The inner seal surface 100 opposes the outer sealsurface 92. An axially extending annular sealing clearance 102 isthereby formed between the inner seal surface 100 and the outer sealsurface 92 of the section 90.

A sloping surface 106 which is adjacent the inner seal surface 100 andwhich is spaced from and parallel to the junction seal surface 96extends at the acute angle 98, relative to the axis 62, to the secondarypump-out vanes 72. An inclined extension sealing clearance or seal gap110 is thereby formed between the surfaces 106 and 96.

In the FIG. 1 construction the recirculation gap 30 is established at aninterface between the impeller 12 and the front liner 36 and extends ina radial direction. In the FIG. 2 case the axially extending annularsealing clearance 102 extends circumferentially around and is parallelto the axis 62. Thus the sealing clearance 102 is coaxial with the axis62. The axially extending annular sealing clearance 102 is followed bythe extension sealing clearance 110, between the surfaces 106 and 96,which inhibits slurry entering through the tube 80 from readily flowingto the secondary pump-out vanes 72 on the front shroud of the impeller.

The prior art arrangement shown in FIG. 1 has a vertical labyrinth sealwhich extends in a radial direction relative to the pump axis. Incontrast the sealing clearance 102 is established circumferentiallyaround and coaxially with the axis 62 and thus provides a horizontalstatic labyrinth seal.

In the pump 50 (FIG. 2 ) adjustment of the front liner 84 in an axialsense relative to the impeller 58 is not called for. The pump 50 is lesssensitive to dimensional changes in the axial width of the extensionsealing clearance 110. Wear effects at the impeller 58 and on the frontliner 84 are significantly reduced due to the axially insensitivearrangement. The flow across the impeller vane passage, (opposing thevanes 72) during flow recirculation, is smoother as the pump is operatedacross its intended performance range.

FIG. 4A illustrates schematically a portion of the pump 50 enclosed in acircle 4 in FIG. 2 . The extension sealing clearance 110 has a crosssectional dimension of X in the axial direction. In FIG. 4B the axialdimension of the extension sealing clearance 110 is increased to 3×.However in each case the thickness of the annular sealing clearance 102in a radial direction is the same. It has been established that the pumpperformance is largely unaffected as the size of the extension sealingclearance 110 varies. Also similar wear patterns are maintained.

FIG. 5 shows performance curves of head in meters, and efficiency,versus flow rate (litres per second) of two pumps under test. The solidlines show the performance curves of a conventional pump. The dotsindicate the performance curves of a pump according to the invention. Animproved head is obtained with a pump according to the invention. Alsothe efficiency of a pump according to the invention is increasedrelative to the efficiency of a conventional pump. These benefits arosedue to a redesign of the impeller primary pump-out vanes which wasnecessary due to the increase in the size of the impeller eye. Theincreased efficiency is demonstrated at higher flow rates. This is alsothe case with the head increase. These factors translate into betteroverall wear and potential energy savings.

The invention offers an improvement of wear life of from 10% to 50% ofthe impeller and of the front liner of a centrifugal pump. The hydraulicperformance of the pump is increased. The operation of the pump is notsensitive to the size of the axial front gap either as establishedduring assembly or as may occur during usage. There is an overallimprovement of wear life and a reduction in energy consumption.

It is possible to implement the principles of the invention in aretrofit manner i.e. to install an impeller and suction inlet structurewhich embody the described concepts, in a conventional pump.

1-4. (canceled)
 5. A centrifugal slurry pump (50) which includes acasing (52) which defines a volute (56) inside the casing (52), animpeller (58) mounted on a shaft (66) in the volute (56), for rotationabout an axis (62), the impeller (58) including a centrally positionedeye (68), a front shroud (74) and a plurality of vanes (70,72) on thefront shroud (74) which extend radially outwardly from the eye (68), anda structure (78) which is mounted to the casing (52) and which isconfigured to supply a medium to be pumped into the eye (68),characterized in that the structure (78) includes a tube (80) which iscentered on the axis (62), a radially extending flange (82) on the tube(80) which forms a front liner (84) and which has an inner surface (86)which opposes the vanes (72) on the front shroud (74) and wherein asection (90) of the tube (80) which protrudes from the flange (82) hasan outer seal surface (92) which extends circumferentially around theaxis (62), which is parallel to the axis and which extends, at leastpartly, into the eye (68), and the impeller (58) includes an inner sealsurface (100) which extends circumferentially around at least a part ofthe eye (68), and which is radially spaced from and which opposes theouter seal surface (92), whereby an axially extending annular sealingclearance (102) which is formed between the outer seal surface (92) andthe inner seal surface (100), and a second sealing clearance (110) whichextends outwardly from the axially extending annular sealing clearance(102), inhibit slurry, entering through the tube (80), from readilyflowing to the vanes (72) on the front shroud (74).
 6. A centrifugalslurry pump (50) according to claim 5 characterized in that the axiallyextending annular sealing clearance (102) is cylindrical with the outersurface (92) and the inner surface (100) which are spaced apart andwhich are parallel to each other and which are coaxial with the axis(62).